The goal of this application is to elucidate the biochemical mechanisms responsible for the modulation of human endothelial cell differentiation in vitro. Specific aims are to characterize in endothelial cell cultures immediate-early differentiation-induced genes and study their expression and possible function during the non-proliferative pathway of endothelial cell non-terminal differentiation. It is anticipated that this effort will provide a more lucid understanding of the biology of the endothelium and the contribution on the non-proliferative aspects of endothelial cell differentiation to the phenomena of angiogenesis.